Fiber board and process of manufacturing fiber board



, Patented Oct. 28,1930

UNITED- STATES PATENT OFFICE noun w. or NEEDEAI, m Josam n. coomnen, 8n, ornaoonnm, man

causms, assreuoas ro momma, me, or aos'rou, mssacnusnms, a common- TIGH- Ol' IASSAGHUSETTS rem-swin This invention relates to fiber board, wall board, and like products which are composed chiefly or entirely of unvulcanized fiber.

It is an important object of this invention Fl so to improve the characteristics of the less expensive ades of fiber board and similar materials t at their serviceability and range of usefulness will be reatly increased, and

to make them suitabli not only 10 uses for which only the better grades of fiber board can now be used, but also to adapt them f0; some urlposes to which it is ignractica to a t emoree ensive a es II The best grades of fiberboard or fiber prodnets are of the so-called vulcanized variety, and this grade of material is very hard, dense,

' and compact. It is a very stable product .and is much used for electrical insulation and ID for mechanical purposes, where it is sub:

jected to severe wear. The lessexpensive grades of fiber board and fiber articles are compressed and consolidated but are not vulcanized, and they are much softer, more por- 2 ous, less resistant to moisture, and warp badly ten ency to disintegrate. While these materials are used as insulators for some purposes,

I0 as for example in enclosed switches, their uses for this purpose are very limited, chiefly because they absorb moisture so readily that their dielectric strength is extremely variable. They withstand mechanical abrasion very poorl and this fact also limits their range of use ess.

Usually these grades of fiberboard or fibrous bodies are composed chiefly of wood pulp, although they may also be made of Other fibers of a woody nature,'as for example, the fiber obtained from bagasse, corn stocks or grasses; but they often contain also a substantial percentage of rag stock or fiber made from rope or twine waste. The composition'ofthose qualities of fiber board with Y which this invention is articularly concerned therefore varies 'consi erably wit and price. I r

I The products of this character which are used as'wall-boards are usually of a rela- Application filed Kay 27,

for many board, and after only a relatively few mothe grade 1927. Serial Io. 194,852.

tively soft character, they have considerable Y aflinity for moisture which often produces buckling or warping, and those of the very porous character usually are also highly. in-

ammable. We have discovered that the characteristic 7 of all of these fiber boards or fiber bodies can be improved vfiy materially b impregnating them with ontan wax. is a mineral wax which usually is imported into this 00 country but is readily obtainable in-large quantities and at a' moderate e use under the name above given. The melting int ofthis wax varies somewhat with 'fierenti grades but usually is in the neighborhood of 180 F., and it has the peculiar property of remaining very hard and brittle as itstemperatureis raised until the melting almost reached, when it passes very rapidly from a solid to a liquid state. One gra e or variation of this waxis known commercially as romalin wax and is also readily obtainable on the market although not so well known as Montanwax. v

The method used in impregnat' fiber board with Montan wax necessarily w vary somewhat with thecharacteristics of the material under treatment and the results de- In treating the softer and more po- A rous grades of fiber board or fiber bodies, such, for example, as wall boards made chiefiy I p from bagas'se fiber, or the like; entirely sat1s-' factory results can be produced simply by soakin the fiber board in a bath of the melted wax, t e bath preferably being maintained at a temperature of somewhere mthe neighborhood of 225 F. At this temperature the wax is absorbed very readily by the fiber ments of immersion, unless the material is un- -commonly thick, it may be removed and allowed to drip.

In treating molded or compressed fiber bodies, or the better grades of unvulcanized fiber board, it is preferable to force the we.

material into the microscopic pores and cc of the fiber board under considerable pres-- sure. For this purpose the fiber board or 'fiber articles may be placed in a l inder or container capable of prea- 100 sures and submerged in the melted wax, air then bein pumped into the cylinder until the desired degree of pressure is produced. Assuming that the material under treatment is fiber board sheets of approximately onequarter inch thickness, a suitable impregnation may be obtained by maintaining the ma.- terial under a pressur of from 100 to 125 pounds for a period of i ne hour, the temperature of the wax being fl om, say, 225 to 250 F. The pressure, time, a id temperature may all. be varied, however, if desired, and as above indicated the exact procedure necessarily will depend upon the nature of the material under treatment and local conditions. A higher temperature facilitates impregnation, and the penetration of the wax also may be improved in treating difficult grades of material-by using a small percentage, say 10%, of some liquid which is readily miscible with, or acts as a solvent for, the wax, such for example, as kerosene, benzol, carbon tetrachloride, or the like. lVhen the treatment has been continued for the desired length of time, the pressure is relieved, and the material is withdrawn and allowed to drain and cool, whereupon the wax hardens or solidifies.

The methods above described produce a high concentration of the wax in the fiber board and greatly increase its weight. If for any reason such an increase in weight is not desired, the fiber board may be placed in the cylinder preparatory to impregnation and subjected to a preliminary air pressure which will substantially fill the microscopic pores and cells in the stock before the melted wax is admitted to the cylinder and allowed to submerge the fiber board. This pressure is maintained while the fiber board is being immersed in the wax, and the pressure then is increased so as to force the wax into the pores and cells of the fibrous body. Later when the impregnation has been completed and the external pressure is relieved, the air held in the pores and cells of the material expands and expels or ejects part of the wax so that the total quantity of wax ultimately retained by the material is reduced.

Fiber board or other fiber bodies which have been impregnated with Montan wax in the manner above described have characteristics and properties which present marked contrast to the untreated materials. The treated stock is harder, more dense and stable. It appears to be entirely unaffected by exposure to moisture and may even be submerged in water for long periods without undergoing material change. Its insulating properties are immensely improved and be,- cause of its greatly increased resistance to the effects of moisture, it can be used for insulation in a great variety of locations where the untreated material would be totally unfit for use. For example, the treated stock can be successfully used in the insulation of the live rails of traction systems and'for a variety of purposes where it is exposed to the weather and where the untreated material would certainly fail. This impregnated fiber product also is highly resistant to the attacks of most acids and will successfully withstand their action for periods of time far in excess of those required to destroy untreated fiber parts. In this respect the impregnated fiber is even superior to vulcanized fiber. Since the impregnated fiber board is substantially unaficcted by moisture it does not shrink, swell or warp when exposed to moisture, and this fact also permits its use for many pun poses where the untreated material cannot be used successfully. Wall boards impregnated in this manner are improved very greatly both because they will not shrink, swell or warp with changes in humidity, and also be cause the board is made much stronger, still'cr, and more stable. The bonding of the fibers together with the wax in addition to the natural mechanical bonding of the fibers with each other, forms a product which is much superior mechanically to theuntreated stock.

The waxy material itself is not readily inflammable so that the porous grades of wall board which are highly combustible are made much less inflammable by the treatment.

In case it is desired to mold the fiber board, or to work it into complicated or unusual shapes, it is preferable in some instances to perform the molding or shaping operation after the board has been impregnated and before it has cooled. For example, in forming curved sheets or flat sheets which are to be used for switch panels, or the like, and where it is desired to have the surfaces substantially true, the impregnated sheets im mediately after coming out of the cylinder may be pressed between dies and held compressed while the wax hardens sufficiently to retain the shape imparted by the dies.

In making some molded articles it is preferable to mix the fibrous constituents in a loose condition with melted Montan wax and thus produce a pulp which is subsequently molded under pressure to the desired shape, the material being allowed to cool in the mold sufficently to cause the wax to set or harden and thus to retain the shape imparted by the molds to the pulp.

A molded stock produced in this manner, or the fiber board impregnated as above described, can be machined with entirely Silt/1S- factory results, the treated stock acting in this respect much like vulcanized fiber.

\Vhile, as above stated, we prefer to use Montan wax, both carnauba and candelilla waxes have properties very similar to those of Montan and can be substituted for it. However, they are considerably more expensive and both have a more pronounced tendency than Montan to shrink or contract upon cooling.

' Other waxes and even oils may be blended with Montan, and oil soluble coloring materials may be used with it. In making any of these blends or mixtures, however, care 7 should be'taken not to reduce the melting point, or more especially the softening point, of the mixture so far that the im- 10 pregnating medium will be liable toooze from the impregnated fiber board, or the surface thereof become sticky or tacky at high atmospheric temperatures, or those temperatures to'which the material must reasonably be expected to be subjected while in use. For ordinary pur oses it is reasonable to expect that treated her board may have to standtemperatures up to 130 or 140" F.

when they are exposed to the sun. Montan 2 wax will not soften'at temperatures considerably-above the latter figure, butin making ing any mixtures of this wax-with oils, other waxes, or the like, it is desirable to hear these temperature requirements in mind. For special uses the temperature limits may vary considerably in'either direction from those above mentioned. We prefer, however, to' make any of these waxy impregnating compounds with at least a predominating percentage of Montan wax.

vSome fiber boards include a very high percentage of fiber made from leather scrap, the percentage varying with the grade of-the board. Usually a considerable percentage of wood pulp, rag stock, or. both, are associated with the leather waste constituents, and in some boards these other ingredients predominate. The characteristics of fiber board of this character can be improved very substantially by the treatment above described, and the article or product resulting from such treatment is improved in substantially thesame respects that have been described hereinbefore.

Vhile' we have herein disclosed preferred embodiments of our invention and preferred methods of practicing the process provided by this invention, it will be understood that j this disclosure has been made rather by way 50 of illustration than limitation, and that the invention is susceptible of embodime t in a considerable variety of forms and .ray be practiced in other ways than those specifical- 1y described without departing from the. spirit or scope of the invention.

and brittle at high atmospheric tem eratures but is sufiiciently fluid at 250 F.-to mto the pores and cells of the fiber body, then allowing the air imprisoned in said pores and cells to expand andthereby to eject a part of forced cally confining said article while it cools to material has hardened.- v

3. That improvement in processes of treat- .hold it in the desired shape until said waxying fiber bodies of a porous character and con- 7 sisting essentially of unvulcanized fiber, which consists in forcing into such a body substantially throughoutv the thickness there- .of a melted waxy material which remains hard and non-tacky at high atmospheric temperatures, subsequently allowing said body to cool sufiiciently to cause said material to harden, and mechanically confining said body while it cools 'to hold it in the desired shape until said material has hardened. Y In testimony whereof we have signed our names tothis specification. 1

ROGER W. CUTLER. JOSEPH R. COOLIDGE, III;

Having thus describcdourinvention, what I we desire to claim as new is:

1. That improvement in processes of treating fiberbodies which consist essentially of 'unvulcanized fiber, which consists in forcing air under pressure into the microscopic pores and cells of said body, subsequently,

while holding said air under pressure in said bores and cells, forcing into said body av 65 melted waxy material which remains hard a so 

